1. Field of the Invention
The present invention generally relates to a washing arrangement for and a method of washing lead frames of semiconductor products such as integrated circuits and large-scale integrated circuits. Still more particularly, this invention relates to removing lead burrs and dam burrs from such lead frames.
2. Description of the Prior Art
During the course of manufacturing a semiconductor product such as an integrated circuit, a large-scale integrated circuit or the like, a synthetic resin or like moldable substance is applied over a lead frame. The lead frame typically has a plurality of leads extending in a longitudinal direction, and a plurality of dams extending between the leads in a transverse direction. The lead frame also has open spaces or gaps in the areas bounded by the leads and dams.
When the synthetic resin in a molten state is applied over designated areas of the lead frame during the manufacture of the semiconductor product, a non-negligible amount of the molten resin overflows from the intended designated areas and spills over onto and attaches, after setting, to portions of the leads and/or the dams and/or the aforementioned gaps. In the art, the overflowed resins attached to the leads are known as lead burrs; and the overflowed resins attached to the dams and/or the gaps are known as dam burrs. These burrs hinder subsequent steps in the manufacture of the semiconductor product. For example, the lead burrs hinder the subsequent plating step in which the leads are plated. The dam burrs hinder a subsequent step of cutting the dams. To counter such hindrances, it is conventional in the art to remove these burrs after the resin molding step.
In one prior art arrangement for removing such burrs, a soft polishing material such as crushed walnut powder is conveyed along a pressurized stream to the lead frame in order to remove the burrs by abrasion. However, the use of walnut powder has not proven to be altogether satisfactory in practice, because the powder strongly attaches itself to the lead frame, thereby requiring a great deal of time, labor and expense to remove and clean the powder from the frame. In addition, large amounts of walnut powder are utilized, and a large-sized recovery assembly is required to recover the powder. A dust collector is also necessary. The size of the overall arrangement is quite large. Furthermore, in the subsequent dam coating step, even small amounts of non-removed walnut powder attached to the dams and/or gaps abrade the cutter, thereby wearing the cutting blade and contributing to a short working lifetime.
In another prior art arrangement for removing such burrs, high-pressure water jets are conveyed to the lead frame to remove the burrs by impact therewith. However, the use of pressurized water in the known arrangements has not proven to be altogether satisfactory, because a lead frame transfer assembly for conveying the lead frames into and out of a washing chamber is located within the washing chamber itself. The atmosphere within the washing chamber is very humid and hot, and the placement of the transfer assembly within the washing chamber leads to many problems. For example, the transfer assembly, having metallic moving parts, is subject to rapid corrosion. Also, inspection and maintenance of the transfer assembly and the overall washing arrangement are inconvenient and time-consuming to perform.